Air conditioning system



Dec. 14, 1954 J. w. MGELGIN 2,696,948

y AIR CONDITIONING SYSTEM Filed April 29, 195o 3 sheets-sheet 1 Dec. 14, 1954 J. w. MCELGlN AIR CONDITIONING SYSTEM 3 Sheets-Sheet 5 Filed April 29, 1950 United States Patent Olce Patented Dec. 14, 1954 AIR CONDITIONING SYSTEM John W. McElgin, Philadelphia, Pa., assignor to `lohn J.

Nesbitt, Inc., Philadelphia, Pa., a corporation of Penn- Sylvania Application April 29, 1950, Serial No. 159,009

12 Claims. (Cl. 236-37) This invention relates to air conditioning systems, and particularly to a method and apparatus for air conditioning and to a control arrangement for controlling the operation of the system.

ln the conditioning of the air in enclosures such as rooms, a common type of unit is one wherein both inside and outside air are blown through heating coils into the enclosure to be heated. By `controlling the supply of the heating medium to the heating coils and by regulating the proportions in which the outside and inside air are admixed, the temperature of the enclosure can be regulated quite closely and a continuing supply of fresh air delivered thereto. can supply a cooling effect to the enclosure when the heating medium is cut oft and the supply of outside air continued. The unit thus acts on both heating and heaterotf cycles for maintaining the temperature of the enclosure substantially constant. Also, at one point in the regulation of a unit of this type, the unit merely recirculates air at no change in temperature. At this time, as far as the conditioning of the air is concerned, the unit is operating on what might be termed idle cycle.

Units of the type referred to above and controls therefor are illustrated in my issued Patents, 2,216,350, granted October l, 1940; 2,268,048, granted December 30, 1941; 2,286,749, granted lune 16, 1942; and 2,290,985, granted July 28, 1942.

Air conditioning units of the type illustrated in those patents and controlled by the control arrangements shown therein have proved to be highly satisfactory so far as regulating the temperature of the entire enclosure. However, in certain instances, notably in school classrooms and the like, at least one wall of the enclosure may consist principally of glass. A wall of this nature, especially when it becomes long as in modern classrooms which are sometimes upwards of fifty feet in length, can create cold drafts adjacent the wall even though the average temperature of the enclosure is maintained at the proper degree.

The air conditioning units referred to are small dimensionally relative to an enclosure which they are capable of conditioning. Thus, the supply of conditioning air from the units is necessarily discharged into the en closure from a relatively small location therein. The cold drafts resulting from the windows can be offset to a certain extent by employing a number of the units spaced along the windowed wall but this is not generally practical because a great deal more conditioning capacity will be embodied in such an installation than is necessar gne way in which the above mentioned cold drafts can be counteracted consists of placing an auxiliary convector, or radiator, along the wall, or distributing convector units along the said wall which will supply heat to the atmosphere and thus offset the cold drafts. Convectors of this type do not employ fans or blowers but operate purely on the convection principle for supplying the additional heat.

l'n attempting to organize an air conditioning system including one or more conditioning units having blowers and auxiliary convector units without blowers, certain dimculties arise which tend to defeat the purpose of the system. For example, if the heating medium to the auxiliary Convectors is so controlled that it is interrupted ln systems of this nature, the unit prior to the interrupting of the supplying of heatingine- 8 vectors will merely act as an aid in the initial warming up of the enclosure, and thereafter substantially the entire load will be carried by the conditioning unit, thus leaving the auxiliary convectors substantially idle. Under these conditions, the same cold drafts referred to previously will be present.

O11 the other hand, if the control system is so arranged that the supply of heating medium to the conditioning unit is interrupted before the supply is interrupted to the Convectors, the conditioning unit will tend to go over to its heater-ofir cycle and the situation will arise where the Convectors are supplying heat to the enclosure and the conditioning unit is supplying cooling air. Under these circumstances, the conditioning unit and the corivectors work in opposition and an inefficient and faulty cycle obtains.

Having the foregoing in mind, it is a primary object of this invention to provide an arrangement whereby blower type conditioning units and auxiliary Convectors can be combined for conditioning the air in an enclosure while operating on a stable cycle.

A particular object of this invention is to provide a combination of a blower type conditioning unit, together with Convectors for conditioning the air in an enclosure such that the conditioning unit and Convectors are prevented from ever operating in opposition.

A still further object is the provision of an air conditioning system for a room such as a school room or the like, which has a tendency toward cold drafts along an outside wall, such that the said drafts are completely offset and eliminated.

Another object of this invention is to arrange an air conditioning system as set forth above and a control system therefor in a practical and simple manner and one which is relatively inexpensive.

These and other objects and advantages will become more apparent upon reference to the following description taken in connection with the accompanying drawings in which:

Figure l is a perspective view showing an air conditioning installation according to this invention arranged along the outside wall of a building such as a classroom or the like.

Figure 2 is a view of a transverse vertical section taken through the blower type conditioning unit and is indicated by line 2--2--2 on Figure 1.

Figure 3 is a vertical sectional view taken through a modified arrangement of providing enclosures for the auxiliary convectors.

Figure 4 is a diagrammatic layout of the air conditioning system of Figure 1 showing the control means associated therewith.

Figure 5 is a fragmentary view showing a modified form which the convector pipe can take, especially when the heating medium is steam.

Figure 6 is a fragmentary perspective View showing one arrangement which can be made of the major and minor heating elements of the conditioning unit in relationship to each other and to the control thermostat of the unit. t,

Figure 7 is a view similar to Figure 4 but showing how the objects of this invention can be obtained by means of a special control system which eliminates the need for a minor heating element in the conditioning unit.

Figure 8 is a sectional view showing the construction of the thermostat which is mounted in the unit of Figure 7 and including a delay yfeature forming an important part of the control system of Figure 7.

Figure 9 is a view similar to Figure 7 but showing still another manner in which the objects of this invention can be obtained by means of a specially adapted control system.

Figures l0 and ll are side and end views, respectively, of a modified type of thermostat for placing in the control system of Figure 9 in place of the two thermostats illustrated as associated with the conditioning unit.

Figure 12 is a view showing a liquid type thermostat which is adapted for replacing any of the thermostats associated with the conditioning units.

Figure 13 is a sectional view showing the construction 3 of a controlvalve that. controlsthe,operationof the dual thermostat arrangement of Figures 9 or l0; and

Figure 14 is a view similar to Figures 4, 7 and 9 but showing how the fans of the unit can be located to draw air through the'heating element by induced draft rather than to blow it through by forced draft.

Referring to the drawings somewhat more in '.detail, Figures l and 2 illustrate an enclosure having an outside wall l@ composed of a plurality of windows l2. Mounted along the wall beneath the windows is a conditioning arrangement according to this invention comprising one or more principal conditioning units as at i4 which comprise fans forblowingair through the units. The arrangement illustrated valso comprises auxiliary convectorsas at 16 and which extend along a substantially greater length of the wall il@ than does the unit or units i4.

A `number `of .different arrangements of the convector or convectors i6 can be made but in Figure l the blower Vunit 14 is abutted on each side by the open cabinet structure-18 which comprises the space 2b extending across the bottom and upthe bach and in which theconvector or convectors is mounted. The lower, forward part of the cabinets .may be provided with the openings or grill work 22 which admit air to space 2t), whilethe upper parts of the cabinets are similarly provided with the openings or grill work 24 through which the heated air may pass. It will be evident that the heated air issuing from the openings 24 will be highly effective for counteracting the cold drafts which move downwardly over the windows i2 thereover.

Figure 2 shows the unit lli in section and it will be seen to comprise a casing having inlet openings 26 through which inside air is drawn into the unit, and an opening 28 through which outside air is drawn into the unit.

Fan means at 3d are provided and the air entering the unit through openings 26 and 23 is driven by the fan through its discharge opening 32 over a main heating element 34- and an auxiliary heating element 36 through the grill 3S in the top ofthe unit.

A roll damper 40 is provided which is movable for adjusting the proportions of air admitted ,through each of the openings 26 and 28 in accordance with practices fully explained and illustrated in connection with the several patents referred yto above.

A thermostat 42 may be positioned as illustrated between the major and minor heating elements for controlling the supply of heating medium thereto, as will be more fully explained .thereinafter.

ln Figure 2 the auxiliary convector takes the form of nned pipe 44 that extends through the dead space 46 at the back of the unit.

ln Figure 3 the convector i6 is arranged along the wall lil beneath the windows l2 and is shielded by relatively small .hood member 48 open at the bottom as at 50 to admit the air to be heated and having openings at the top as at 52 for the discharge of the heated air.

Turning now to the control system of Figure 4, wherein the various parts of the conditioning system and the control system are identified by the same reference numerals employed in Figures l and 2, the control medium employed is iiuid pressure obtained from a compressor and pressure tank as illustrated in my Patent No. 2,268,048, but it will be apparent that the controlmedium could be electricity7 or a liquid medium such as hydraulic uid, if so desired.

In Figure 4 there is a room thermostat at `6() and to which is supplied air pressure by conduit 62. Air discharges from the room thermostat 60, this arrangement being well known in the art and being such that if the temperature of the room or enclosure increases, the pressure in conduit 64 increases, whereas if the temperature decreases, the pressure in conduit 64 decreases.

Conduit 64 of Figure 4 is connected directly with valve operator 66 of control valve 68 of the minor heating element 36. Control valve 63 is located in conduit 76 that supplies steam or whatever heating medium is being employed to heating element 36. According to this invention, element 36 is relatively small and may consist of bare pipe or of pipe with a relatively small number of tins thereon so that the temperature rise encountered from main heating element 34 through the minor element is only in the neighborhood of l degrees Fahrenheit.

Conduit 64 is connected through restrictor 72 with a conduit 74 that has one branch leading to thermostat 42 and another branch leading to the damper operator 76. Damper operator 76 controls damper 4i) in accordance with theparticulartype ofheatingcycle beingreinployed. Normally, the damper is closed to the outside air until the temperature in the enclosure comes up to a predetermined point. Thereafter, the damper may move to admit all outside air, to admit a minimum quantity of outside air, or may be so controlled as to maintain a predetermined mixture of inside and outside air. The particular type of control exerted over 'the damper forms no part of this invention in itself.

The thermostat at 42 may be ofthe type illustrated in Figure l0 wherein there is an outer tube Si? within which there is mounted a rod 82 anchored in the tube at one end and free in the tube at the opposite end. The tube preferably has a high coeiicient or' expansion whereas the rod S2 preferably has a much lower coeicient of expansion. Suitable materials for these members are brass for the tube Sil and Invar or a ceramic material for the rod 82. ln any event, the rod .82 will shift axially of the stationary end of the tube in response to temperature changes.

The lbranch of conduit '74 leading yto the thermostat terminates in a jet Vor leak port 84 adapted for being variably restricted by pivoted plate 56 having an adjustable set screw 8S bearing on the end of rod 82. A spring 9u normally urges theplate toward the leak port.

The thermostat is preferably arranged with a portion of tube 8l) exposed to the air passing from element 34 to element 36, and another portion, as at 92, exposed to the outdoor air entering the unit. The purpose of this is to compensate for changes in temperature of the outside air whereby uniform control of the temperature of the enclosure is obtained.

It will be evident that thermostat 42 operates to permit the exhaust of iiuid from leak port S4 at a rate generally inversely proportional to the temperature to which the thermostat is exposed. When the rate of leakage from the port is high, there is a pressure drop on downstream side of restrictor 72 and when the rate of leakage is reduced, the pressure on the downstream side of the restrictor tends to approach the pressure standing on the upstream side.

The major heating element 34 is adapted for having heating medium supplied thereto through conduit 94 in which is located control valve 96 adapted for adjustment by operator 98 that is connected to receive pressure from conduit 94. In connection with both of the valves 63 and 96, they are normally urged toward a wide open position and are adapted for being closed by their respective operators 66 and 98 in response to increasing pressures in conduits 64 and 74, respectively.

In Figure 4, the heating medium discharged from element 36 is conveyed by conduit lill) to convector i6 to act as the heating medium for this element also. lt will be apparent, however, that the elements 36 and t6 couid be connected in parallel for being controlled by valve 68, or each could have its own individual control valve and fully equivalent results would obtain.

Operation of the nwdijcatz'on of Figures I through 4 Let it be assumed that the enclosure to be hea-ted is cold and that the conditioning system of this invention is .placed in operation. Under these circumstances the damper 40 will be swung to cut off all air from the cutside and the valves 68 and 96 will be wide open so that a maximum supply of heating medium will pass to the heating elements 34 and 36 and to convector i6. The enclosure is thus warmed up and as the Vten'lperature thereof increases, room thermostat 6i? brings about an increase in pressure in conduit 64. This pressure is transmitted to the thermostat 42 and, when it reaches a certain value as determined by the throttling effect set up at the leak port of the thermostat, will cut oit maior heating element 34.` At or prior to this time the damper 4t) has moved to some intermediate position as determined by the type of cycle for which it is adjusted.

The conditions now obtained are that minor heating element 36 and convector 16 are both supplying heat to the enclosure. The purpose of having heating element 36 supply heat is that it prevents the unit 14 from having a cooling effect on the enclosure which would tend to counteract the heating effect of the convector 316. Also, by placing heatingeiement 36 on the downstream side of thermostat 42, the heat supplied by the said element does not interfere with the operation of the thermostat so that major heating element '34 remains cut off when the room temperature approaches a predetermined point.

If the heat supplied by mnor heating element 36 and convector 16 is sufficient to cause a further increase in the temperature of the enclosure, then heating element 36 and convector 16 are also cut off by closing of valve 68. Thereafter, the control of the system is the same as that which obtains in other systems with the thermostat 42 controlling the supply of heating medium.

From the foregoing. it will be apparent that the combination of the unit conditioner and Ventilating unit and the convector are so controlled that they never operate in opposition and that the heater-off cycle of the condi- -tioning unit obtains only when the convector is on its idle cycle. At any time that the convector is supplying heat to the room, heating element 36 is also receiving heating medium and is supplying heat to the room. This arrangement results in a very stable operation and at no time is there a loss of efficiency due to the unit and convector operating on contrary cycles.

The heating medium employed may comprise hot water or steam, and when steam is applied, the construction illustrated in Figure 5 for convector 16 may be employed to advantage. In this figure, the main convector pipe is at 110 and the steam supplied thereto is by means of aI central pipe 112 which delivers the steam to the opposite outer ends of the convector, the condensate from the convector being drawn olf from the center thereof. An advantage which is gained by this arrangement is that the heating of the enclosure by the convector comes from the ends of the room, rather than from the center part thereof to which heat is already being supplied bythe conditioning unit 14. l

Figure 6 illustrates an arrangement somewhat more compact than that illustrated in Figure 2 and wherein the minor heating element 36 is placed directly on top of major heating element 34 and with the center part of heating element 36 left open as at 114 for lreceiving thermostat 42. The thermostat may be suitably shielded against inuence by the heat of minor element 36, and, under these circumstances, the same sort of operation obtains as with the construction of Figure 2.

Modcations of Figures 7 and 9 In the modification of Figures l through 4, the objects of this invention were obtained by the addition' of an on its idle cycle.

In the modifications of Figures 7 and 9, the objects of this invention are obtained without the use of the additional minor heating element in the conditioning unit, and, instead, the unit is prevented from going on a heaterolf cycle while the convector is supplying heat to the room by special arrangements of the control system.

Making reference first to Figure 7, the major yheating element therein is indicated at 150 and the convector at 152. Valve 154 having the operator 156 controls the supply of heating medium to element 150while valve 158 having operator 160 controls the supply of heating medium to convector 152.

Positioned in the air stream leaving heating element 150 is a thermostat 162 which is illustrated more in detail in Figure 8. This thermostat has the conventional outer tube 164 and inner rod 166, the differential expansion of which adjusts a plate 168 in the manner already described to accomplish the variable throttling of leak port 170 connected with conduit 172.

point for plate 168 are mounted on an arm 174 pivoted at 176. This arm is urged 1n a direction to decrease the restriction of leak port 170 by spring 178 and is adapted for being urged in the opposite direction by a bellows` arm 186, pivoted at 188, and urged against a iixed stopk rod 190 by a spring 192.

The thermostat of Figure 8 operates as follows: When the enclosure is cold and the system is placed into operation, a minimum of restriction of leak port 170 obtains due to the contracted condition of tube 164 and` In Figure 8, however, the leak port 170 and the pivotvk 70 this, together with the fact that the room thermostat is supplying a minimum pressure to conduit 172, results in a low control pressure that permits the heating medium supply valves to stand fully opened. As the temperature of the enclosure increases, and as tube 164 expands, arm 174 moves counter-clockwise about its pivot by the expansion of bellows 180 and plate 168 moves toward position to increase the throttling elfect at the leak port 170. However, before the pressure in conduit 172 reaches the value which will cause the supply valve for the main heating element to close, the lower end of arm 17 4 abuts set screw 184. This will halt further movement of arm 174 until after a predetermined greater pressure rise takes place within the bellows 180. The amount of this pressure rise can be determined by adjustment of spring 192.

During the time that the pressure in bellows 180 is increasing due to the operation of the room thermostat as the temperature of the enclosure rises, the control valve for the convector is moving toward its closed position and this valve will become completely closed before the pressure in bellows 180 overcomes spring 192 and moves arm 194 to cause a pressure rise in conduit 172 that will close off the main heating element.

Turning again to Figure 7, the room thermostat referred to is indicated at 194 and pressure is supplied thereto through conduit 196, with the pressure supply from the thermostat going to conduit 182. A branch conduit 198 leads from conduit'182 to operator 160 on valve 158 and another branch in which restrictor 200 is mounted connects with conduit 172 leading to leak port 170, operator 156 of valve 154 and damper motor 202.

As an example of a typical schedule of pressures and temperatures which might obtain in connection with the modification of Figure the thermostat 162 could be so adjusted that the pressure in conduit 182 could rise to 7 pounds per square inch in order to bring arm 174 against `set screw 184. The throttling of leak port at that -stat reached a pressure of, say, 1l pounds per square inch. At this time the pressure in bellows would overcome spring 192 and the restriction of leak port 170 would increase, thereby developing a high pressure at valve operator 156 and bringing about closing of valve 154 after a predetermined further pressure rise.

It will be evident from the foregoing that the arrangement of thermostat 162 is such that there is a hesitation in the closing of valve 154 as the temperature of the enclosure rises. During this period of hesitation, the control pressure in the pneumatic control system rises and will close off valve 158 of convector 152. In this manner the heating unit is prevented from going on a heaterolf cycle while the convector is in operation. The convector thus carries its proper share of the conditioning load and is never operating in opposition with the conditioning unit.

In Figure 9 there is illustrated still another arrangement for controlling the operation of the combined unit ventilator and convector. In Figure 9 the unit ventilator has only a major heating element as indicated at 250 and the convector as indicated at 252. Valve 254 having operator 256 controls the supply of heating medium to the heating element 250 while valve 258 having the operator 260 controls the supply to the convector. The room thermostat is indicated at 262 and air is supplied thereto through conduit 264, the said air discharging from the thermostat through conduit 266. Conduit 266 has a branchv line leading to valve operator 260 and another branch line leading to valve operator 268 of a control valve 270 to be described hereinafter.

Conduit 266 has still another branch leading through restrictor 272 to valve 270, to valve operator 256 and .to damper operator 274.

In the modification of Figure 9, two thermostats are provided as indicated at 276 and 278. Each of these thermostats is of the standard leak type as illustrated in Figure 10 and which construction has already been eX- plained in connection with the first modification of this invention. These thermostats are connected to valve 270 by conduits 280 and 282, respectively, and the said valve is operable for automatically selecting the one of the thermostats which is to be effective for exercising control over the operation of the conditioning system. The valve .270 .and the .operator therefor .are :shown in :somewhat .moredetail in Figure :13. .lnFigure 13 ,it 'twill -b'e :noted .that valve :2/0 .comprises a :valve .member .284 -.which will connect either one or the'otherof conduits '.280 and 2&2 with the branclrconduit connected with thedownl lows:

yDuring the time that theenclosurebeing heated has comeup to temperature, oneoffthethermostats y276 .and 278is`in .control of the systemtdue-to the .position occupied by valvemember 284 of 4valve :270. This thermostat .is -set for some ,predetermined .temperature range which .may be, lfor example, -75 `to-.tSO-.degrees Fahrenheit. With this thermostat in .controllof :the-system when the .temperature in the enclosure y.approaches lthe value for which the thermostat that is .effective-is adjusted, :the control valve 254 .of heating IelementfZSt) willlclose.

Following this, if no adjustments .are jmade in the thermostat control, the Ventilating .unit will go on a-cooling cycle and thus oppose fthe actionof convectorlSZ. However, at substantially the same pressure at lwhich valve 254 is lclosed by its operator.256, operator 258 actuates valve `member 284 of valve 270 to .-its other position thereby making the .other one =of thermostats 276 and 278 effective. This other thermostat is set-for a substantially lower control temperature, for example,

a value of 11 pounds -per square inch. During the ltime i that the control pressure 1s .increased from 7 pounds -to 1l pounds, valve 25S -is being closed yby is operator so that by the time the Ventilating unit actually changes over to a cooling cycle, the supply of `heating fmedium :to the convector iscompletely cut olf. It will be evident that the organization of Figure 9 also achieves :the -ob 'Y jects of this invention Vbypreventing vthe f'Ventilating unit and the convector from ever operating inopposition.

The two thermostats 276 and-278 may advantageously be built into a single unit as illustratedin Figure I10 wherein the rod-82 is adapted for-actuating plate 86 which lmay either be a single plate as described in connection with Figure 4 and which may be a double plate vasindiCatedYat l86a and-86h in Figure 11. When two l'plates are employed each may control a different yjet as at `84aandr84b.

The thermostats which Ahave been described in Aconnection with the several modifications of this invention are all adapted for being partly'di'sposed inthe vincoming outdoor air stream and lpartly disposed -in the heated stream of air from the major 'heating element. Figure 12 shows a fluid pressure type tthermostat `wherein vbulb 300 may be positioned in the 'outdoor stream and 302 positioned in the heated air stream. The pressuregenerated acts through bellows 304 to actuate Irod 306 for shifting plate 308 that controls jet 310, The Vthermostat construction of Figure 12 is adapted for inclusion in any of the systems described.

All of the systems described up 'to this point are of the blow-through type wherein the yblast of air through `the Ventilating unit is forced through by 'blower yrneans on the upstream side of the heating element. However., this invention is also adapted for being practiced in connection with a draw-through type unit such as is illustrated in Figure 14 where the blower means 350 is positioned on the downstream side of heating element 352. It Will be evident that all the features described in connection with this invention would be perfectly adaptable to the type of unit indicated in Figure `14.

I claim:

1. In an air conditioning system, a main conditioning.

8 .unit having `a blower and yvertically-spacedrmajor and minor heating elements, fan yauxiliary unitcomprising a convection heating elementpositioned :apart from said main-unit, meansforconducting a supply offheati-ngmedium'to'said heatingelements including a separate conductor forsaidmajor unit and a common conductor for said-'minor and auxiliary units, means for controlling the 4vsupplyof heating medium in each or said conductors comprising a rst thermostatic means positioned apart .fromfsaidfmainunit and responsive to rises-in temperature'to decrease the supply to'said units, a second thermostatic means positioned 1n said maln unlt'and responsiveftofrises in temperature for interrupting said supply tof-said major element at a predetermined temperature `ri1se,-said rst thermostatic'means interrupting the-supply lin -saidcommo'n conductor upon a further temperature rise subsequent to interruption of said major unit.

2. In-an air-conditioning system, a main conditioning unit having a Eblower and vertically spaced major yand minor heating elements, an 'auxiliary unit comprising a convection -heating .element `positioned, apart -frorn said Vmain vunit,lme`ans for-conducting a supply of heating mediumto said heatingelements including a separate -conductorfor saldi-major unit and a common conductor for `saidfminorrand auxiliary units, valve vrnea'ns in each of said rconductors, means for controlling the 'supply of heating l.medium in each of said conductors comprising a 4ilirst thermostatic means .positioned apart-from said main unit .andresponsive to rises in temperature Ito vpartially close said valves, a-secondthermostatic-rneans positioned inl said main unit and responsive to Arises in temperature .forcompletely closing the valve in said separate conductor at a predetermined temperature rise, said iirst thermostatic means completely closing the valve 4in said comymonrconductor.upon a further temperature rise subsequent to -closure of said separate conductor valve.

3. .-Infan air ffcondit-ioningsystem for'an enclosure hav- -ing Windows therein, a vmainconditioning unit having a `.blower vand verticallyspaced vmajor and ,minor heating 'ele1nents,-an 'auxiliary unit having -an lelongated convection v.heating element adapted for being positioned on either side of saidi'main unit and beneath said windows, means for supplying heating medium to said major and minor heating elements, means for conducting said heating 'medium from said-minor element lto said auxiliary unit, valve "means for controlling the -supply -of vheating medium to veach 'of said main `heating units comprising y'first thermostatic `means in said enclosure positioned apart from saidmainunitand responsive to rises in tem- `perature to decrease the supply to said main units, second thermostatic means positioned in said main unit and responsive to "rises in temperature for 'interrupting said supply to said major element at a predetermined temperature rise,-said vfirst thermostatic `rneans interrupting the supply to 'said minor and auxiliary units upon a Eurther temperature rise subsequent to interruption `of the supply to said lmajor unit.

v4. =In van air conditioning Asystem for fan enclosure having lwindows therein, a main conditioning `unit having a blower and vertically spaced major and minor heating elements, said minor element being -of a smaller capacity than said major unit, auxiliary units comprising elongated convection heating elements adapted for positioning beneath the windows of said enclosure ion either side of 'said main unit, a common supply of heating Amedium for said major and minor units vand means for Condireting said medium thereto, said auxiliary units being connected `in series with said minor element for common iiow of heating medium'therethrough, means vfor controlling the supply of heating medium to vsaid lunits comprising a first thermostatic 'means located 'in said enclosure apart from said 'main lunit and responsive to rises iin temperature to decrease said supply, a second thermo- :static `means positioned in `said main unit and responsive to rises in temperature for 4interrupting said supply to main major unit only at a predetermined maximum temperature, said -iirst thermostatic means lbeing operative to interrupt said supply to said minor and auxiliary units only after interruption of the supply to said major unit and upon a temperature rise above sa'id predetermined maximum.

5. In an a'ir conditioning system, a main conditioning unit having a blower fand vertically spaced major and lminor. heating elements, an auxiliary unit comprising an elongated convection `heating element, means for supplying heating medium to said main heating units comprising a common source for said medium and including valves at the inlets to said main units, means for conducting heating medium froln said minor unit to said auxiliary unit whereby the heating cycles of said minor and auxiliary units will be in exact synchronism, pressure means for opening and closing said Valves, a rst thermostatic means spaced a substantial distance from said main unit for controlling said pressure means, a second thermostatic means connected to said pressure means and positioned adjacent said major element for actuation thereby, said second thermostatic means operable to close the valve to said major unit only on a predetermined temperature rise thereof, said first thermostatic means operable to close the valve to said minor element upon a rise in temperature beyond said predetermined temperature.

6. The combination of claim wherein said second thermostatc means comprises a leak port connected to said pressure means and a bimetallic element extending in the heated area above said major unit, said bimetallic element being operable on expansion thereof for closing said port. v

7. The combination of claim 1 wherein said minor and auxiliary units are connected in series to said common conductor.

8. The combination of claim 1 wherein said minor and auxiliary units are connected in parallel to said common conductor.

9. The combination of claim 1 wherein said second thermostatic means comprises a leak port and a bimetallic element positioned in said main unit above said maior element and operable on temperature rise to close said port.

10. The combination of claim 1 wherein said second thermostatic means comprises a leak port and a pair of iluid pressure generating bulbs, one of said bulbs being positioned in an outdoor air stream and the other of said bulbs being positioned in said main unit above said major element and bellows means for closing said port upon a rise of pressure generated by said bulbs.

11. The combination of claim 1 wherein said blower is positioned beneath said heating elements and acts to force air upwardly toward said elements.

12. The combination of claim 1 wherein said blower is positioned above said heating elements and acts to draw air upwardly through said elements.

References Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 961,734 Powers June 14, 1910 1,913,681 Otis June 13, 1933 1,914,712 Ewald June 20, 1933 1,928,737 Otto Oct. 3, 1933 1,941,314 Otto Dec. 26, 1933 1,941,315 Ward Dec. 26, 1933 2,076,399 Carson Apr. 6, 1937 2,205,349 Dube June 18, 1940 2,268,048 McElgin Dec. 30, 1941 2,411,295 Saballus Nov. 19, 1946 

